Servo valve bypass



Aug. l1, 1953 .1. R. CLIFTON 2,543,313

sERvo VALVEA BYPAss A Filed June 9, 1952 5 Sheets-Sheet 1 27 ank/rf Fran/e Magg@ f//s frn/r rraA/ve Aug 11, 1953 J. R. CLIFTON 2,648,313-

sERvo VALVE BYpAsS 1Nl i o Jp,

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naive-ff Aug- 11, 1953 J. R. CLIFTON 2,648,313

VslazRvo VALVE BYPASS Filed June 9, 1952 3 sheets-sheet s .6,00 a m1/z ffm-A65) :standpoint of the pilots Patented Aug. 11, 1953 UNITED STATES PATENT GFFICE SERV() VALVE BYPASS vJohn R. Clifton, Rolling Hills,A Calif.,zassignor to Northrop. Aircraft, Inc., :Hawthorne, Calif., `a corporation of California 'Application June 9, 1952, Serial'No 292,411

4 Claims. 1

Myinvention relates'to means for controlling .rate gain in hydraulic .power systems, and more particularly to animproved means iorby-passing hydraulic uid in a hydrauliccontrol valve to. control therate-gain in a hydraulic system.

' In .the copending. application of Feeney, 'Serial No.,23,567, led April 27, 1948, now abandoned,

`there .is shown a complete highpressure `hydraulic control system for operating attitude control surface in an aircraft solely by hydraulic .power under control of the pilot. In this system each hydraulic power unit, whichnormally. in-

cludesl -a piston driven within a cylindersby hydraulic' fluid from aconstant pressure source to -operate an attitude control surface, is actuated by. a neutral leakageY type controlvalve vwhich is usually yintegrally .mounted on the rhydraulic 'motor cylinder. yThe -control valve is properly designed to provide, at the neutral position thereof, .a predeterminedfiuid ow of relatively small magnitude fromA the pressure supply port .to bothof the hydraulic motor operating ports while: simultaneously .allowing an equal .flow from theoperating ports to a'. system returnfport. VIn

a` 2000 p. s. i. system, for example, theneutral leakage passages ofthe valve described aboveare designed to create a 1000 p. s. i. preload kineach operating port fand, therefore, on each yside of the-.piston of the valtitude control'` surface actuating motor lto provide. a required surface control rigidity lat all` times during yoperation of .the

system. The valve just described is shown,- described, and claimed byiStrayer in thefcopending `applicationf-Serial No. V123,37i' ,.1iled October 25, 1949, now Patent No.'2,612-,872.

Therate ofnuid flow 'roma constant:y pres- 4sure source into and out of a1 hydraulic Vmotor cylinderin a hydraulic system isfgenerally expressed by the term piston velocity, `and the term gain as used'herein is dened as meaning the ratio'of `valve displacement,y i. e. travelfdisin the ideal system,v gain -should be veryl-lownear theneutral position or the valve, andfinthe-full A open. position range. of the/valve, the .gainshould xberelatively high, as was: described inthe copending-application of :Strayer and myself, -Serial No.f.228,'716,. led May-28, 1951, ofswhich applica- -tion my. presentinvention is a continuation-inpart.

Vas to cperateonly during the tlf, in the "itype Tof :fhydraulic control system undery 'discussiomlthe'means for` reducing gainin the. system. is made tobe effectivel nearv the `.neu-

.tral 1 position rv only' of! the. control valve, it isi' possible to have fullsystem pressure available Anear v1the"'f.ull openpositi'on of the=valve,fa feature which is highly desirable. Therefore, it is one of y.the yobjects ofmy `present invention tofprovide an improved'cmeansffor ycontrollinggaineinf-la 'hydraulic full` power control system.

It 'is another.A object of my v'invention to provide .a' means of.; controlling gain in' ay high pressure hydraulic.airplanecontrol systemfwhich lis eiective only'near the Aneutral 'positionI of-a control valve,so that full system pressure is alwaysavaillable inthe full^open position range of the valve.

' Other objects and features will .be-apparent `as thel specification continues.

Briey, the`by`pass=-means of mypresentinvention, i inf one embodiment thereof, 1 takesA the kform of f a 'by-passmeans integrally associated with the 'metering l lands of a valve: spool in a lneutralileakagetype control valve, 4and movable `with the' L valve fspoorV overthe.` meter-ing holes of a fixed valve sleeve in thevalve, so that 4asthe 'metering lands traverse the metering holes ofthe sleeve during travel` of the spool awayfrom. the neutral k.position thereof, the byf-pass means comes intoV alignment with the lmetering holesfo .the sleeve to Vby-pass acontrolled amount of the nuid `flowing 4.through the valve to the-motor cylinder, intol the return -passage of thevalve; the

fluidthus byfpassed being controlled to an i amount tdgive thefpropergain reductionto pro `duce-the', maX-imumstability .inl the system. -The by-pass means is. so positionedein the. spoolI lands initial. travel ofthe spool from*v neutral, I bei-ng vinoperable when the .full open vposition range yof the valve is approached.

.To Hfacilitate v.a ful-1er understanding of my present f' invention the accompanying .draw-ings are provided wherein:

Figure. lisv a. schematic diagram vin perspective of a portionf of. -a full. powerairplane. hydraulic control` system;` the-portion of acontrolsurface shown `being `an aileron.. for` example.

Figure .2 A.is 'fa fragmentary longitudinal sectional View of` the` neutral leakage control valve and/motor; the vsizeof the motor in kproportion to the'valve being greatly reduced.

Figure 3 is.. a framentary enlarged. schematic view. inl4 longitudinal`4 section of a portion of the valve of Figure 1, to .-.more .'clearly. showthe .by-

passmeans ofthe. present-inventionas ident'iied by lX andl Z.

Figure 4 is a fragmentary view in perspective of the valve spool of the previous figures, showing one preferred construction of the by-pass means.

Figure 5 is a coordinate diagram charting the comparative flow curves of the valve of the previous figures with and without by-pass means.

A portion of one form of a full power control system which is highly suitable for airplanes in the 600+ M. P. H. class is shown in Figure l, where a pair of aileron power units I are operatively connected to move an aileron I2 which is normally located in the wing panel of an aircraft (not shown). A hydraulic pressure line I4 and return line I5 connect into servo control valves I6 connected to each outboard power unit I0.

The aileron power units I0 and servo valves I6 of each unit are identical and therefore only one unit will be described in detail. Each power unit I0 is composed of an actuating cylinder I1 having its piston rod I9 projecting forwardly and pivotally secured to structural fittings attached in the wing panel (not shown). The closed end I6 of the cylinder I1 connects directly to an aileron pivot fitting 2| above an aileron hinge line 22.

A valve housing 24 is connected with the actuating cylinder I1, or is made an integral part thereof as in the present case, and encloses an inner valve assembly 25 as is best shown in Figure 2. The clevis 26 end of the valve assembly 25 extends out one end of valve housing 24 to connect to a valve operating rod 21 as shown in Figure l.

Referring again to Figure 2, in the actuating cylinder I1 the piston rod I9 carries a piston 29 operating in a cylinder chamber 30 having cylinder operating supply passages 3I at each end thereof. Supply passages 3I lead to outer fluid grooves 32 in the valve assembly 25 which comprises a fixed sleeve 34 and a hollow valve spool 35 slidably mounted therein. Each outer fluid groove 32 connects with the interior of the sleeve 34 by means of extremely small radially drilled fluid flow metering holes 36 which are each located in a staggered pattern relative to each other, lengthwise of the sleeve 34. A ring of relative large pressure ports 31 are provided through the approximate center of the sleeve 34 and are radially and circumferentially arranged therearound to communicate with a pressure inlet bore 39 in the valve housing 24, which also connects to one of the pressure fluid lines (not shown). Opposite one end of the sleeve 34, a return bore 40 also communicates with the interior of sleeve 34 and with a return line (not shown).

The valve spool 35 has a peripheral pressure groove 4I therearound and positioned opposite the sleeve pressure ports 31, and return grooves 42 on each side of the pressure groove 4 I.

On the spool 35 metering lands 44 separate the spool grooves 42 and 4I and are located opposite the respective sets of sleeve fluid flow metering holes 36 when the spool 35 is in neutral position. The spool return grooves 42 connect with an axial spool bore 45 which communicates with a number of radial spool end passages 46 by which return fluid reaches the housing return bore 40.

The two outer edges of each metering land 44 are completely square cornered and hardened to such a degree as to be capable of shearing any foreign particles which might be carried into the valve in the hydraulic fluid. The spacing of the center line of each land 44 is equally spaced with the center line of the metering hole patterns so that the pressure inlet 39 always communicates with one side of each metering land, and the fluid outlet 42 always communicates with the other side of each metering land 44. Thus movement in either direction of the spool 35 away from neutral position causes fluid flow openings 36 to be serially uncovered to connect one side of the actuating cylinder piston 29 to pressure through one of the cylinder supply passages 3|, and to connect the other side of the piston 29 to return.

The metering lands 44 with respect to openings 36, are properly spaced and constructed so as to allow a predetermined balanced leakage to pass through the openings 36 to both sides of actuating cylinder piston 29 and the same balanced leakage from both sides of the piston 29 to the return bore 40, when the valve spool 34 is in neutral position.

It should be mentioned that the valve is not, per se a claimable part of the present invention as it forms the subject of the above mentioned Patent 2,612,872 to Strayer, but is described in detail so that the function of my by-pass will be more easily understood.

Referring again to Figure l, each valve operating rod 21 is pivotally connected to a bell crank 41 which is rotatable about a fixed axis 49 and a solid linkage 50 connects each bell crank 41 to a common bell crank arm 5I rotatable about a quadrant axis 5,2. A cable control quadrant 54, xed to rotate with the crank arm 5I, carries an aileron down cable on one side thereof and an aileron up cable 56 aflxed on the opposite sides thereof; these cables passing over pulleys 51 and running to a pilots control stick 59 in the conventional manner. A centering spring assembly 60 connected from a point on the control quadrant 54 to the wing structure (not shown) provides the required control stick centering forces.

-Also pivotally connected to each bell crank 41 and moving in the same direction, is a pushpull rod 6I similarly connected to one of two synchronizing quadrants 62 which are commonly connected to rotate together by closed circuit synchronizing cables 64, so that when the aileron control cables 55 and 56 move the linkages 50 and the respective bell cranks 41, the standby cables 65 are likewise moved therewith.

It can be seen from the above description of the full power control system, that relatively small movements of the control stick will move the control surface. Not shown, of course, are other mechanisms for changing the ratio of stick movement to surface movement, artificial feel producer, backlash removers etc. which are necessary in such control systems in high speed aircraft. It will be immediately apparent, however, in such a control system, stability is particularly critical. To that end then, the by-pass means of my present invention is directed.

To reduce gain in the system near the neutral position of the valve, I provide a by-pass means, one form of which is shown in Figures 2, 3, and 4 at X and Z. Each land 44 of valve spool 35 of Figure 2, as best shown in Figures 3 and 4, is provided with a groove 10 which preferably extends completely around the circumference of the outer periphery thereof and is spaced approximately equidistant between each shearing edge thereof. A single bore 1I is drilled in the bottom of the groove 10 at any point around the circumference of the land 44; the bore 1I being sized to about .013 inch in diameter in the present example, and extending from the bottom of groove 10 to the interior of spool 35. The width of the groove 10 is made slightly wider than the diameter of bore rame rs 1|. 'Itrshould be-noted inligure3,i'thatforthe sake of clarity, the' cylinderf supply rpassages`3| are shown at the topv ofvalve blocki24 r-whilei the pressure inlet 39 is shown in-normaLrelationrto the valve. In this view fluid isfsupplied through I pressure inlet 39 and-enters a pressure'groove--SB of thesleeve Y34, and isthen admitted lthrough pressure ports V31 in groove`38 to the pressure groove 4| between the landsl44;cnspool v35. 'i It can now beseen that when spool'35 isin neutral,

Aas shown,vthe flow hole`36 (schematicallyshown in dotted lines) at each en'dfoffthe-patternf'of :flow holes is bisected to permita small flow therethrough andv across the openingsof the cylinder chamber pressure passage 3|; a likefamountlf ow being returned through return grooves 42 on the outer sides of lands 44. Thus a balanced pressure is continuously maintained on each side of the piston 29 in the cylinder I1 during neutral.

As the spool 35 is moved away from neutral, the lands 44 traverse the flow holes 36, serially opening the fiow holes on one end of sleeve 34 to increase the flow to one pressure passage 3|, at the same time serially uncovering the flow holes 36 on the other end of sleeve 34 to admit return ilow from the cylinder through pressure passage 3| of the corresponding end thereof. Inasmuch as the ratio of spool 35 movement over the flow holes 36 is directly related to flow rate, and ow rate to piston velocity and gain as was explained early in this specification, it is apparent that the by-pass bore in the groove 10 on the particular land 44 on the pressure side, by-passes a portion of the flow from the pressure inlet 39 directly into the inner chamber 45 of the spool 35 and thence to return; reducing the rate of gain in the system. It should further be noted that by the time the inner edge of the land 44 on the pressure side of the valve spool 35 has approximately cleared the center flow hole 36, the bypass bore 1| will have cleared the outer end flow hole and is, for the balance of the spool travel toward full open position, inoperative. It is therefore obvious that full system pressure is resumed for the full open position range of the valve.

In addition to providing the required gain reduction in the system, the by-pass described above has been found to have a desirable damping effect in the valve, especially during operation of the system when there is an absence of load on the control surface, such as when the airplane is on the ground, for example; a highly desirable feature in a high pressure hydraulic system of any kind.

The simple construction of the by-pass bore 1 I from a manufacturing standpoint is more clearly shown in Figure 4.

The flow curve evolved by incorporation of the by-pass bore 1| in the valve of the previous figures is shown in Figure in a coordinate chart 12 plotting the curves which reflect the gain in the hydraulic system as the valve is moved from neutral in either direction. The vertical ordinates '|4 represent spool travel in decimal fractions of one inch, and the horizontal ordinates 'l5 represent decimal fractions of one gallon per minute of flow as the valve is opened to either side of the actuating motor.

Curve A of the chart reflects the performance of the valve of Figure 2 without any by-pass means. It can here be seen that as the valve spool is displaced from neutral, a relatively steep curve results indicating a sharp increase in gain as the spool moves through the first .02 inch of ,.6 travel yover kthe :flow thole @pattern of the evalve sleeve. .The.ba'lance'.of 'thecurve 3A ofcourse iin'dicatesfsubsequent increasesas .the spoolmoves r4to' full; open position. )The sharp increasesinrate .gain thus shown, can. indicate instability Ain the system.

With the by-passrmeans of :the present invention incorporated into the valve, the .flow ycharacteristics Vthereof Vevolves .curve B .which ushcwsfa .denitereduction in v,the slope rof the curve. from neutral to about ..06 inch 'of `spool ftravel; the. desired Vresult sought. kFrom .06 inch toward full 'position'curve B' blends. into `curve .-A fas the. by-passv moves ioutl .of range of the flow holefpatternand intorthe'range of full open position .of Athe :.valve 4to .indicate .that full system pressure isthen=available in the system.

.'Ithas thusbeenshown thattthe by-passmeans .,of'myzpresent invention ,satisfactorily fulfills the functions desired in a high pressure'hydraulic system, as shown by curve B which substantially illustrates the ideal curve sought in such a system, while being relatively simple to incorporate into a valve of the type described and shown herein. Further, manufacturing costs and time in connection with such means are relatively negligible.

While in order to comply with the statute, the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specic features shown, but that the means and construction herein disclosed comprise a preferred form of putting the invention into effect, and the invention is therefore claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims.

What is claimed is:

1. In a hydraulic control system of the character described including a neutral leakage valve, a hollow sleeve xed in said valve and having a fluid pressure inlet therethrough, said fluid pressure inlet comprising a plurality of relatively large, radially and circumferentionally aligned holes through the wall of said sleeve, a fluid outlet from the interior of said sleeve around an end thereof, two operating cylinder passages through said sleeve on opposite sides of said pressure inlet, each of said cylinder passages consisting of a plurality of extremely small metering holes positioned radially through said sleeve around the periphery thereof and all staggered relative to each other lengthwise of said sleeve, a hollow spool member matching the interior of said sleeve and movable in either direction from a neutral position, the interior of said spool communicating with the return outlet of said valve, two metering lands on said spool and contacting the interior of said sleeve and having the two outer edges thereof completely square cornered, the spacing of the center lines of said lands equaling the spacing of the center lines of the cylinder passages, said pressure inlet always communicating with one side of each metering land, and said fluid outlet always communicating with the other side of each metering land; means for reducing rate gain in said system, comprising means associated with each of said metering lands and movable therewith over said metering holes to by-pass a portion of iiuid from said pressure inlet directly into said fluid outlet.

2. Apparatus in accordance with claim 1 wherein said means for reducing the gain in said hydraulic control system defines at least one by-pass channel extending through each metering land of said spool, between the interior of said sleeve and the interior of said spool, whereby when said by-pass channel is aligned with one of said metering holes of said sleeve, a portion of said fluid from said pressure inlet is by-passed into the interior of said spool.

3. Apparatus in accordance with claim 1 wherein said means for reducing gain in said hydraulic system comprises a groove on the outer periphery of each of said metering lands and extending completely around the circumference thereof, and means defining a bore, one end of said bore opening in the bottom of said groove, the other end of said bore opening in the interior of said spool, whereby when said groove is aligned with one of said metering holes of said sleeve, a portion of said fluid from said pressure inlet is by-passed through Said bore to the interior of said spool.

4. Apparatus in accordance with claim 1 wherein said means for reducing gain in said hydraulic system comprises, a groove on each land and positioned equidistant from each edge thereof and extending completely around the circumference thereof, and means defining a by-pass channel through each land, the opening at one end of said channel opening in said groove and the opening at the other end of said channel being positioned in the interior of said spool, whereby when said groove is aligned with at least one of the metering holes of said sleeve, a portion of said fluid from said pressure inlet is by-passed through said channel to the interior of said spool.

JOHN R. CLIFI'ON.

No references cited. 

